Shadow helps Sans
by mikeyismine4ever
Summary: It's Shadow's thanksgiving break, and even though she's upset her uncles won't be able to hang, she excited for a week of normality...but with her life that's just not possible, when she finds a short skeleton in her room she finds out that she now has to go on this huge adventure without any help...so much for normal.
1. Prolog

_(Kimmy) This is a crossover, Shadow is April and Casey's daughter...incase you didn't know that. Anyway, while I work on a chapter for another story , I will also be working on this one. Enjoy. ..please._

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"Have a good Thanksgiving break." I waved by to my friends as I walked through the door of my mom's shop.

"How was school?" Mom asked and I shrugged.

"Boring as usual." I said watching her as she worked behind the counter.

"Your dad's going to be home late tonight. Your uncle Raph called and the two of them want to go 'dragon bashin' tonight." Mom said and I rolled my eyes as a smile split my lips.

"Is Uncle Mikey coming over?" I asked as I followed her into the storage area.

"Uncle Mikey can't come over. Your aunt Angel asked him to put his human afire to good use to go to a college party." Mom said before leading me to the front of the store again.

"Okay…what about Uncle Donnie?" I asked smiling thinking of helping him do science stuff.

"He promised to spend the week with Leatherhead, and I'd really rather you not be there. We both know how those two get." April said chuckling I gave a small laugh. "And before you ask Leo is visiting Usagi."

"I'm heading up to my room." I said frowning a little. "I'm sure I can figure something out to do." She nodded and I ran up the stairs and into my room. There's only two bedrooms here….mom and dad finally decided to share a room. I close the door with a smile, sure I was a little upset about my uncles being busy, but that meant one very good thing for me, I finally get a week to be normal. I close my bedroom door and look around my room trying to see what to do, my eyes land a small figure my the window, who ever it was, they were staring out the window, wearing a blue hoodie with the hood pulled on, black shorts, and slippers on.

"Sure is a nice day ain't it?" He said turning around, I then noticed that he had a skull for a face and I frowned. Great…there goes my week of normal.

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 _(Kimmy) There's he prolog, let me know if I should upload the 1st chapter. I know it's hot and I'm sorry, the next chapter will be longer i promise._


	2. A chat and rules

_(Kimmy) Here's the first real chaptet...thing. Disclaimer I do not own TMNT or Undertale_

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"Get out, get out." I said trying to drag the guy with the skull head out.

"Gezz kid, that anyway to great a new friend?" He asked and I stopped pulling on his arm and let it go. He was right, I was raised better, tossing people out the second I see them, grandfather would be ashamed. I sighed and faced him. "I'm Sans. Sans the Skeleton." He reached a hand out to shake hands.

"I'm Shadow. Shadow Jones." I said before reaching and grabbing his hand to shake it. I froze as a loud noise cane from out hands. I let go and he burst out laughing before showing me a tiny Whoopi cushion on his left hand. I smiled and laughed a little to. "That's good, I'll have to use it on my Uncle's."

"You're probably wondering why I'm here." Sans said walking over to my bed. "I need your help."

"With what?" I asked as he sat down, I remained standing in front of him.

"Getting home." He said. "I need to travel dimensions to get home."

"Joy, look skely, I just wanted a normal, thanksgiving break. Ya know away from all the monsters and crazy of my life." I said.

"I ain't exactly thrilled either kid. But my 'pal' error thought yanking me from my dimension and tossing me here would be fun." Sans said and I saw the small whites of his eye roll around his eye sockets.

"What do you expect me to do?" I asked. "I can't travel through dimensions." He shrugged. "Why did he toss you with me? I have an idea, I think I know who might be able to help you."

"Who?" He asked I quickly crossed the room to dug through my backpack and pulled out a shell shaped phone.

"My uncle Donnie should know what to do." I said dialing his number.

"NUH uh. ThAt WoUlD be CHEATING."A voice said and my shell-cell suddenly disappeared. I blinked at my now empty hand before rounding on Sans.

"Hey, I'm trying to help you." I said he help up his boney hands in surrender looking as confused as I was.

"It wasn't hiiiim." A voice said I turned and saw a black glitchy version of Sans floating above the window. "I D..don't LiKe CHEATers." I gulped as he glared at me. "You and YOU alone are going to get H….h..him home." A creepy smile spread across his face before he vanished.

"But I can't travel through dimensions." I said hoping he would change his mind.

"Not MY proBLEM." His voice said and I slumber my shoulders.

"Ugh, fine. Okay…uhm….Mr. Glitchy –" I was cut off as the figure reappeared in front of me.

"My n-n name is ERROR." He said glaring at me.

"Right…s..sorry. What are the rules?" I asked. "I need to know so I don't break them."

"You…a….and you ALONE a….ar…are his only help. G…g..good luck." Error said smiling evilly. I frowned. "I….it's nOt as HARD as you're making It ssseem, oh and I made IT To where Iffff Sans gets to FAR he will DIE. Good lUcK." He disappeared.

"Looks like we're stuck with each other. Let me pack and we'll be on our way." I said before walking over to my closet and pulling a big duffle bag and packing it full of stuff. Sans just watched. "What? You didn't think I'd just give up did ya? We're making a trip to Nevada. Bishop's old base is there, he don't work there anymore so technically we aren't 'cheating.'" I smiled as I saw him stuff his hands into his pockets.

"You gonna tell your parents?" Sans asked and I shook my head.

"Are you crazy? It'll be fine, they used to do this kind of thing all the time, dad said so." I said as I walked over to the window. "It'll be fine. Now come on, we've got a long way to go." He just shrugged and followed me out the window, I'd be back in no time.

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 _(Kimmy) please review. I am trying with this story._


	3. The adventure begins

_(Kimmy) So, I got review saying they didn't understand what Error was trying to say, well he basically said that they could not ask for help, they aren't aloud to tell anyone. And Error sent him to Shadow because, he just wants to be jerk. Anyway, here's the next chapter._

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If your planning on crossing the country, make sure you have a plan, one that does not include walking from New York, New York to Nevada. We got 3 blocks when we found out that walking would take too long, and we needed to hide Sans from people…I was getting tired from all the weird looks he was getting, so was he. I mean his hood was still up…and he was still getting wired looks!

"And your sure this isn't cheating? Cause I don't really feel like getting another visit from Error." Sans said as he look around the window of the Turtle-copter.

"We didn't ask for it did we? Then it's fine. Now be a pal and disable the tracking thing." I said as I continued to hot wire it. Soon we were taking through the air.

"I disabled it." Sans said as he buckled up. "How did you learn to fly this?"

"My Uncle Mikey taught me….so did my Uncle Raphie. Mom stopped the lessons after a while though." I said. "Not sure why." Sans remained quiet as he looked over the city as we flew over it.

(No POV)

"April, I'm here." Mikey said walking into living room followed by Angel

"Oh good." April said turning and facing the blonde hair boy and the purple haird girl. "You still have your human disguise on." Mikey gave her a confused look.

"Well ya, I mea. We were about to leave when you called." Angel said.

"So, Shadow's not with you?" April said looking between the two. They shook there heads.

"Maybe she went down to the lair." Mikey suggested. April shook her head.

"She would have told me." April said.

"Maybe she did and you just didn't hear her." Angel said, April thought it over and soon the 3 of them were on their way to the lair.

"Of course I tried that, it's been disabled. No, I don't want you to cut your trip short." Donnie was talking on his phone to Leo when April, Angel, and Mikey walked in. "Yes. It's gone…don't wwry I'll…figure something out….uh huh…yea…bye." He hung up and looked at the 3 people staring at him.

"What's up?" Mikey asked.

"The Turtle-copter is gone, and the tracking device has been disabled." Donnie said and April started to freak out a little.

"Dtn worry April, I mean it's not like she can fly the thing." Angel said. Raph walked into the room about rhat time. "So her being gone at the same time as the Turtle-copter could be a huge coincidence." Mikey and Raph shared a look.

"We may have taught her a thing or two." They said at once. "We told her not to take it till she learned to land though."

(Back with Shadow)(Shadows POV)

"I gotta ask, why did he

"Your staring." Sans said and I looked away from him and back to the sky. "Don't worry kid, I know this a skeleTON of stuff to take in."

"It's fine. So, what happened?" I asked I saw him tense out of the corner of my eye.

"Let's just focus on getting to this 'Bishop's' place first. Okay kid?" Sans said.

"I'm sorry." I said. "Okay well, I need something to fill the void." He tensed again but I continued talking. "And since you won't tell me your life story, I'll just tell you mine. The reason I was so ready to kick you out, without even hearing what you had say, my uncles, and my parents both had crazy stuff happen to them. Mom said my uncles saved her more than once…my dad said he saved them a lot…my uncle smacked and said not to lie to me. I was soooo excited to he following in there foot steps, so happy to be going on adventures. But nonce I started school, I heard everyone saying weirdo like it was an insult, I want to be normal, my uncles were always worried about be called freaks…that they would never be excepted by humanity. I want to be excepted…like they couldn't." I stopped talking. "Sorry."

"Don't be. Look nothings wrong with being different. Think about it, would your pals be more impressed with you getting a good grade on a test or…saving an entire monster world?" Sans asked. "They way I see it, you've got a monster of chance of it being the latter." I laughed.

"Do all you know is monster puns?" I asked.

"Nah, I got a ton more….a skeleTON more." Sans said and I couldn't help but laugh. We flew well into the night, it was early the next day when I noticed the welcome to Nevada sign. I continued flying, I felt my eyes get drippy and start to close. "Hey! Kid the ground…" My eyes popped open and I pulled us up.

"Maybe we should land and walk the rest of the way." I suggested. "Besides it'd be easier to get into the building." I pointed at a long building off to the side.

"Great, so land this thing so we can start demension hoppin." Sans said, I frowned.

"I…I don't know how to land. I didn't get that far into the lesson." I said I gave Sans a sheepish smile and he looked like he was thinking of something.

"Okay, try to land it, if something starts goin wrong….well we'll cross that bridge when we come to it." Sans said. I gulped as I started to lower the helicopter.

(A little while later)

"That could have gone better." I said as we walked over to the building.

"Not to sure you uncle's gonna be too happy about his copter." Sans said pointing back to the destroyed mess that used to be the Turtle-copter.

"Well we wouldn't have needed it if you had told me about your teleporting powers, we could have teleported here." I said glaring at the small skeleton. When Sans noticed I was not going to be able to land the copter safely we grabbed my shoulder and a blue aura sounded us, next thing I know I'm on the ground, it took hearing the crash of the Turtle-copter to relies what has happened.

"Ya, well, let me explain how it works. Unless I know the destination, I can't teleport to it. There's no tellin where we'd end up if I tried." Sans said and I sighed.

"Welp, let's get this over with. Let's get you home." I said smiling. We got in no problem, I mean the place was deserted after all. Finding the right room however, that was proving to be difficult since, I'd never been there myself.

"I'm starting to get the feeling you have no idea where ta go." Sans said as we approached another dead end.

"This wouldn't be so hard I'd the place wasn't a wreck and we could wall 5ft without hitting a collapsed wall." I said a little annoyed.

"If ya wait a minute maybe I can help." Sans said. "I'm gettin tired of all this runnin around." I was about to ask him of he had any other plans his left eye glowed a bright blue, he lifted his left hand witch was now blue, he pointed it at the blocked path, I turned and saw him use his magic to lift the blockage. I smiled with glee as I saw what looked like science stuff. "Well don't just stand there, is that the place?"

"Ya, come on." I said running under the stuff into the room. A loud crash sounded behind me, I turned and saw Sans standing there, he had dropped the pile of junk behind him. After searching several rooms I finally found what looked to be the right room. "Finally!" We quickly looked around the room until we came across a small portal like thing.

"Whats that? Is that the portal? We xabr fit through that." Sans said obviously annoyed.

"You think I can't see that?" I said before looking around. "Lift it up, let me see if anything on the bottom or-" I froze as he used his powers, a blue glow surrounded the small portal but it did not move, the portal activated, the last thing I saw was a bright light, then everything went dark.

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 _(Kimmy) Please review and let me know what you think, the reviews let me know you like what in writing._


	4. Underfell

_(Kimmy) This chapter is WAY longer then I meant for it to be, but I had too many ideas that I couldn't waste. Anyway, enjoy...DISCLAIMER I do not own TMNT or Undertale...or any of the undertale AUs._

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*Thud* "Ow." I said as I sat up and started shivering. "Why is it s…suddenly s…so c….cold."

"We're in Showdin." Sans said helping me up. He gave a concerned look as I continued shaking. "Here kid, this'll keep ya warm, it'll make ya look, cool as well." He winked at me as he handed me his big blue hoodie. I quickly slid it on and instantly felt so much warmer.

"Since you know where we are, we must be close to your home, which means, I can go home." I said smiling while still shivering slightly.

"Ya, well sine Error won't 'grace' us with his presence, I guess it's up to me to send ya home." Sans said making quotation marks in the air with his finger…bones. "Come on, I know a way to get ya back, we'll stop at me la-" He stopped mid word, I looked at him and saw staring at something with a mix of surprise, confusion, and anger. It's was like I was looking at 3 of my uncles at once. I followed his gaze and saw….another skeleton that looked shockingly like Sans.

"Whose that?" I asked pointing to the short skeleton.

"Great, of all the places to get sent to, it had ta be this one." Sans grumbled. He turned me, his faced softened when he saw my confused look. "Just, stay close kid. New plan, this isn't my home, its….it's an alternate version of my home."

"Oh, makes sense, then that must be an alternate version of you, right?" I asked giggling at the shocked expression on his face. "My uncle's a scientist." The white of his eye sockets vanished at the word. I looked away, for some reason, that look was terrifying, and I don't know why.

"Right, of course." He said before starting to walk, after he took a couple steps he turned around and looked at me, his eye sockets were showing the whites dots that made him look….less threatening….I guess. "Ya coming kid? We can't get ya home, until we get me home." I walked over to him. "Don't worry kid, I'll keep ya safe."

"And whose gonna keep you safe bonehead." A voice said we faced front and saw that the other version of Sans was now standing in front of us.

"Hey red, how ya been?" Sans said…I understood why he called him red, he was wearing a red and black jacket…that looked very soft on the inside, black and red shorts, a red sneakers (not tied). He had one gold tooth and the rest of his teeth were sharp…like shark sharp. He had a crack right above his left eye socket.

"Same as always original. Whose the kid?" Red asked pointing at me.

"Kid? I am not a kid." I said. "I'm in middle school." I stuck my tongue out at him….he stuck his younger out at me… it was bright red. I hid behind Sans.

"What? She started it." Red said. "Now, again what are you doing here? You know boss doesn't want you to visit. He threatened ta dust ya last time." I blinked in confusion at that.

"I know, I know. We didn't expect ta come here. We need to find a portal….you wouldn't hopped ta have one would ya?" Sans asked.

"No, absolutely not, ya think I'd be able to hide stuff from Boss as easy as you can from Papyrus?" Red asked shocked sounding.

"True, do ya think Alphys has one?" Sans asked. I looked at him confused still.

"Yea, but good luck getting permission ta use it." Red said shrugging.

"Oh, we ain't askin for permission, in fact were hoping she won't even know we're there." Sans said.

"SANS! YOU LEFT YOUR STATION AGAIN! WHEN I FIND YOU…" Red gave a horrified look as the voice disappeared.

"Ya know what, how about I escort you two to te hotlands?" Red offered.

"Sounds good ta me. What'd ya say k..Shadow?" Sans asked looking back at me. I stepped out from behind him.

"I trust you, and if he's a version of you, then my default I trust him." I said, Red look confused, but Sans smiled bigger and nodded.

"Sweet, she's on bored. Let's go." Sans said, before we even took two steps, time around us froze.

"WHOA." All 3 of us looked up.

"Great, ya brought this bag of bones with ya." Red said his left eye glowing brighter. Sans left eye sparked a bright blue as well.

"Hi Error!" I yelled waving and smiling at him. Red and Sans looked at me like I'd lost my mind.

"Uh..h. Hi." Error said sounding confused. "Anyway, I S..SAID. No OuT Side helllllp."

"I know, and technically we aren't breakin no rules." Sans said crossing his arms with a smug look on his face.

"HE iS not aloud TO help." Error said crossing his arms.

"Nah uh, that's not a rule." I said before pulling out a notebook. "You said it had to be us….well you say those exact words, but you did say me and me alone, but you contradicted yourself, cause I need Sans' help to do anything, so with that info that I gathered you basically said the only I can have is from Sans." I point at Red, "And he technically IS A Sans. So he's aloud to help." I stuff the notepad back into my backpack. Error had this dumbfound expression on his face before shaking his head and glaring at us.

"Fine. WhAtEvEr. I Don't care." He disappeared and time started up again. He seemed….upset that I found a loophole in his challenge. Red and Sans high-fived and we continued walking. All through Snowden, I was freezing still, the coat kept me pretty warm…but-

"Geez kid, all that shaking ya doin is gonna give away our position." Red said. "Here, this'll be warmer than Original's." He took off his big puffy jacket and handed it to me, he was wearing a red long sleeve shirt. I slid the puffy jacket or the front half of my body, Sans hoodie was on my back half. I was warm and toasty…..all the was into the hotlands…

"It burns!" I said yanking the jacket and hoodie off and on to the ground.

"Geez Kid, ungrateful much?" Red asked picking up his jacket and slipping it on.

"You could have warned me." I said.

"Kinda though the name 'Hotlands' would give it away." Sans said slipping his hoodie back on. I rolled my pants legs as we continued walking.

"Okay, Alphys lab is right there." Red said pointing to a building.

"Awesome, how do sneak in?" I asked.

"Like hell I'm doing that." Red said. Sans left eye flashed blue before going back to normal when I started talking.

"What if we make a deal. One you'll be crazy not to agree to?" I asked they both looked at me, and since we are hiding in a bush, it was pretty funny looking.

"I'm listening." Red said.

"If you help us, I'll convince you brother, not to get mad at you and you'll get the next day off your job….if you have one." I said crossing my arms and smiling.

"Fine, but you help me first." Red said glaring at me.

"Fine." Sans said. "Let's hurry this up, I kinda wanna get home."

"And you better not be lying, or else, I'm going to be have a great time." His eye glowed a bright red.

"D...don't worry, my uncles taught me to negotiate." I said.

"Good, let's go." Red said grabbing mine and Sans' shoulders. A red glow appeared around us, next thing I know we're in a bedroom. "My brother will be home soon, so what's your plan?"

"Oh, uhm….I don't have one." I admitted sheepishly.

"WHAT!" Red yelled causing me to flinch. Sans used his magic and pulled Red away from me. "You said you'd make him not mad at me."

"I'm not going back on my deal, I just don't have plan, my uncle Mikey said the best way to negotiate is to wing it, which is what I-" A loud bang startled us.

"Let's hope this works." Sans said.

(Mikey's POV)

"That was mean, I mean, we were teaching her a life skill." I said rubbing my sore cheek. "My cheek still hurts from that slap."

"Ya what was that for?" Raph asked rubbing his cheek.

"I told you those lessons were dangerous and that I didn't want her learning to fly it until after she turned at least 18."

"You act like we told her, 'Hey Shadow, here a fun idea, why don't you fly the copter now, you know when you don't know how to land!' Does that sound like something we would tell her?" I asked. April's glare made me turn my chair around. April was currently driving the battle shell, no we had no idea where Shadow went, but that wasn't going to stop April. She took me and Raph with her because, she needed backup, and she was still mad at us. I was trying to think of how to get her to not be hate me and Raph. "Hey, I think I might have way to know where she went. We can't track the copter it's self, but April had Donnie install a tracking device on to Shadow's phone. Why don't we track that?" April slammed on the breaks making me fall out of my seat….should have worn my seat belt.

"Why didn't think of that?" April asked herself out loud. I leaned over to the dashboard, turned on the GPS Donnie modified and looked up Shadow's phone, the last location it transmitted….was Nevada?

"Hey, that near Bishop's old place." Raph said. April smaller on to the gas pedal sending me and Raph flying back, we quickly climbed into out seats and buckled up.

(Shadow's POV)

"And that is why you should give him the day off." I finished, I could Red shaking behind me, Sans was glaring at Red brother left eye glowing bright blue.

"HMM, I SEE YOUR POINT, THIS WOULD HELP HIM WITH STEALTH, IF HE PULLS IT OFF ANYWAY, VERY WELL, IF THIS BUMBLING IDIOT PULLS IT OFF AND ALPHYS NEVER KNOWS HE WAS THERE, THEN HE MAY HAVE TOMORROW OFF, AS WELL AS GET OUT OF PUNISHMENT TONIGHT." The brother said.

"Thanks boss." Red said looking a little more relaxed.

"BUT," We froze as he continued. "WHEN HE FAILS?"

"Uhm…I dun know, you can uh…have my soul or something." I said getting a gasp from Red and Sans, Sans also visibly stiffened.

"I ACCEPT THE DEAL." He said smiling evilly, Red teleported us back to the bushes we were hiding in before, I was hoping they would relax, but they just looked more stressed.

"You offered you soul?!" Red growled. "What are ya, stupid or somethin?"

"Hey, give the girl a break, she doesn't know the rules down here." Sans said, trying to sound calm but his eye was still a bright blue, though not as bright as when we were with Red's brother.

"Will one of you bone heads tell me what the shell is going on?" I asked making them both turn there heads to me.

*sigh* "Taking your soul is not a joke, his bro will kill you and take your soul, he will use to become head of the royal guard." Sans said. I gulped.

"This is so stupid, ya can't risk your life for me to get a day off." Red said.

"Yes I do, besides it's not just for the day off, you 'bro' was going to beat you wasn't he?" I asked and Red looked a bit nervous before going into defense mode.

"It's to toughen me up." He said, though his voice shook a little.

"Besides, my uncle always said that he'd do anything for his friends even if it meant they would be the ones to get out alive and not him, always do anything and everything you can to protect your friends, so that's what I'm going to do." I said, they both looked at me like I had lost my mind.

"Well, if she trusts you can do it, then so do I. Come on buddy let's get this over with."

(A few minutes later)

"I'm starting to regret this, I am terrified right now." I whispered as I followed Sans and Red through an airvent.

"Chill kid, Alphys never checks these." Red said.

"Alphys is a terrifying monster yes, but I'm more worried about this thing breaking under all our weight." I said.

"I've been up here plenty of times, it's a good place to hide from boss when I need space." Red said.

"Ya, but now not only is there two of you, but we also got Shadow with us." Sans said point back at me.

"Oh, right." Suddenly the vent creaked and broke.

"Ow." I said sitting up. "Great plan Red."

"Shh, someone's coming. We gotta hide." Red said. I stepped between them hooked my arms around there's then pressed a hidden button on my purple bracelet.

"Don't move." I whispered they didn't say anything but I felt them both tense as a scary looking yellow dragon monster walked into the hallway we stood in. After looking around for a whole the monster left.

"I..I can't believe it, how did she not see us?" Red asked as I repressed the button letting go of the skeletons.

"My Uncle Donnie made me this bracelet for the 7th birthday, it has a built in force field, and it can turn me invisible plus who ever I'm touching as well. It's for protection." I said.

"That's…actually pretty awesome." Sans said giving me a big smile.

"Come on, we gotta keep looking." Red said making me look away from Sans, Red looked very happy as we made out through the lab avoiding Alphys (I learned that was her name) and we soon found a room with a portal in it. Red closed the door behind us.

"Wait, how are you going to get out with being spotted?" I asked.

"Don't worry bout me kid." Red said.

"No, she's right, you bro ain't gonna say it counts if you just teleport back home." Sans said.

"I know, but-" A loud bang outside the door interrupted him.

"Here's use this." I said sliding the bracelet over his boney wrist.

"I can't take this." Red said.

"Don't worry, you need it more than I do." I said. Sans use his powers to activate the turned off portal. We got sucker into the portal, last thing I saw was Red looking relaxed as he activated the bracelet.

"You didn't have to do that." Sans said as he floated through the demension time stream….thing.

"I know, but frankly I'd rather him not get beat then my keep a bracelet my uncle can easily replace." I said.

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 _(Kimmy) I'm having then go through same different AUs. I did underfell first cause after the original it's my fav, if you have any idea one where r hey should go next, let me know. Please review thank you. :)_


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